Battery packs are widely used that have a plurality of primary or secondary battery cells, a circuit board, and a battery case encasing these components. When an electrolyte solution leaks from any of the battery cells, it can corrode the wiring of the circuit board, resulting in a conduction failure or short circuit. To prevent such corrosion and short circuits when leakage of the electrolyte solution occurs, a liquid absorbing element containing an absorbent capable of absorbing the electrolyte solution is arranged in the battery pack adjacent to or in the vicinity of the battery cell (Japanese Patent Application Laid-Open No. 2001-351588). Various polymer materials are used as the absorbent, including adsorbents, gelling agents and self-swelling agents. Among specific examples of the absorbents described are polyacrylate-based water-absorbing resins, starch/graft copolymer-based water-absorbing resins, polyvinyl alcohol-based water-absorbing resins, polyacrylamide-based water-absorbing resins, isobutyrene-maleic acid copolymer-based water-absorbing resins, long chain alkyl acrylate crosslinked polymers, and polynorbornens.
One drawback of these absorbents is that they cannot effectively absorb propylene carbonate, dimethyl carbonate and other carbonate-based solvents that are widely used in nonaqueous electrolyte battery packs, a type of batteries that have become increasingly used in recent years. Specifically, these solvents are used in nonaqueous electrolyte secondary cells that make lithium ion-based nonaqueous electrolyte secondary battery packs.
The present invention addresses the above-described problem and to that end, it is an objective of the present invention to provide a liquid absorbing sheet capable of effectively absorbing the nonaqueous electrolyte solution used in nonaqueous electrolyte secondary cells that make nonaqueous electrolyte battery packs (in particular, lithium ion-based nonaqueous secondary battery packs). It is another objective of the present invention to provide a battery pack equipped with an electrolyte-absorbing element made of such a liquid absorbing sheet.